Process for manufacturing high density press-formed articles

ABSTRACT

HIGH DENSITY PRESS-FORMED ARTICLES MAY BE FORMED FROM A POWDER MIXTURE, CONSISTING PREDOMINANTLY OF HIGH ALLOY METALS, WHICH CAN BE FORGED ONLY WITH DIFFICULTY, IF AT ALL. A PREPRESSED WORKPIECE IS FORMED FROM THE POWDER MIXTURE AT A PRESSURE OF ABOUT 6 T./CM.2, AND IS THEN HEATED TO BETWEEN 800 AND 1100*C. THE HEATED WORKPIECE IS THEN COMPACTED OR DEFORMED AT A PRESSURE OF ABOUT 8 T./CM.2 IN A PRESS TOOL WHICH HAS BEEN PREHEATED TO A TEMPERATURE BETWEEN 150 AND 350*C. AND WHICH IS HELD CONSTANT AT THIS TEMPERATURE DURING THE COMPACTING OPERATION. THERE IS NO SINTERING OF THE WORKPIECE IN THE PRESS TOOL. THE RESULTANT PRESS-FORMED ARTICLE MAY THEN BE ANNEALED IN A VACUUM FOR 4 TO 5 HOURS AT 1250*C.

United States Patent 3,605,245 PROCESS FOR MANUFACTURING HIGH DENSITYPRESS-FORMED ARTICLES Gerhard Zapf, Krebsoge, Germany, assignor toSintermetallwerk Krebsoge G.m.b.H., Krebsoge, Rhineland, Germany I NoDrawing. Filed Oct. 8, 1969, Ser. No. 864,902 Claims priority,application Germany, Nov. 26, 1968, P 18 10 883.3 Int. Cl. B221? 3/24U.S. Cl. 29-4205 3 Claims ABSTRACT OF THE DISCLOSURE High densitypress-formed articles may be formed from a powder mixture, consistingpredominantly of high alloy metals, which can be forged only withdifiiculty, if at all. A prepressed workpiece is formed from the powdermixture at a pressure of about 6 t./crn. and is then heated to between800 and 1100 C. The heated workpiece is then compacted or deformed at apressure of about 8 t./cm. in a press tool which has been preheated to atemperature between 150 and 350 C. and which is held constant at thistemperature during the compacting operation. There is no sintering ofthe workpiece in the press tool. The resultant press-formed article maythen be annealed in a vacuum for 4 to 5 hours at 1250 C.

This invention relates to a process for manufacturing high densitypress-formed articles in which a preheated prepressed workpiece iscompacted or deformed in a preheated press tool.

It has been proposed to heat a prepressed workpiece consisting mainly ofiron powder, without sintering it, to a temperature between 800 and 1100C., and then to compact it in a press tool which has been preheated tobetween 300 and 350 C. and is then held at constant temperature. Theproduct has a comparatively high density between 7.4 and 7.8 g./cm. Theprocess does not involve the usual time-dependant sintering. Theprepressed workpiece is merely heated to between 800 and 1100 C. andthen compacted in a press tool which has been preheated to between 300and 350 C. The temperature gradient between the preheated press tool andthe workpiece remains substantially constant and in consequencerecrystallisation conditions are always the same. This applies inparticular to the series production of compacted articles, where theprepressed workpieces follow each other in rapid succession through thesame compacting tool.

It has now been discovered that the proposed process mentioned earlieris suitable for manufacturing high density press formed articles notonly from prepressed workpieces consisting mainly of iron powder, butalso, and with the most excellent results, from prepressed workpiecesmade of powder alloys which cannot be forged, or only with difficulty. Afurther discovery is that the process can be conducted at even lowerpressed tool temperatures.

According to the present invention therefore, a process formanufacturing high density press-formed articles from a powder mixturepredominantly of high alloy metals which can be forged only withdifficulty if at all, comprises forming a prepressed workpiece from thepowder mixture, heating the workpiece to between 800 and 1100 C., andcompacting or deforming the heated workpiece without sintering in apress tool which has been preheated to a temperature between 150 and 350C. and which is held constant at this temperature during the compactingoperation.

Preferably, the workpiece is prepressed under a pressure ofsubstantially 6 t./cm. and the final compacting operation is conductedusing a pressure of 8 t./cm. The

temperature of the preheated press tool is held constant during thecompacting operation by controlled cooling.

The process in accordance with the invention may be called powderforging, and compared with conventional forging processes such as dieforging an advantage of this process is that it can be used formanufacturing press formed articles having good mechanical strengthsfrom raw material substances which cannot be forged by conventionalmethods, or at least only with difficulty. A further advantage is thatthere is no waste product and no flash is produced in the press-forming.The press-formed articles made by a process in accordance with thepresent invention are more accurate in their dimensions than thoseproduced by conventional forging methods. Internal passages and complexexternal shapes can be produced with high accuracy. Finally, the hotdeformation can be obtained with less consumption of deformation energy,compared with conventional forging processes.

The compacting step may, if desired, be followed by annealing thepress-formed article for 4 to 5 hours at 1250" C. in a vacuum.

Several examples of the production of press-formed articles by a processin accordance with the present invention will now be described.

EXAMPLE 1 Starting out with a mixture of electrolytic iron powdercontaining 5% chromium powder, 59% nickel powder and 26% molybdenumpowder, a prepressed workpiece was formed under a presure of 6 t./cm.The prepressed workpiece was heated to 850 C. and then compacted under apressure of 8 t./cm. in a press tool which had been preheated to 350 C.and then held constant at this temperature. The resulting product had adensity of 8.51 g./cm. The product was then annealed in a vacuum forfour and a half hours at 1250 C. After annealing the product showed atensile strength of 48 kp./mm.

EXAMPLE 2 A prepressed workpiece was formed under a pressure of 6 t./cm.from a mixture of electrolytic iron powder containing 16% chromiumpowder, 57% nickel powder, 17% molybdenum powder and 4% tungsten powder.The resulting prepressed workpiece was preheated to 850 C. and compactedunder a pressure of 8 t./cm. in a press tool which had been preheated to350 C. and was then held constant at this temperature. The product wasannealed in a vacuum at 1250 C. for four and a half hours, the finalproduct having a density of 8.78 g./cm. a tensile strength of 39 kp./mm.an elongation at rupture of 6.4% and a Brinell hardness of 120.

EXAMPLE 3 A prepressed workpiece was formed under a pressure of 6 t./cm.from a mixture of electrolytic iron powder containing 1% chromiumpowder, 65% nickel powder and 30% molybdenum powder. The prepressedworkpiece was heated to 850 C. and compacted under a pressure of 8t./cm. in a press tool preheated to 350 C. and then held constant atthis temperature. The resulting product was annealed in a vacuum at 1250C. for four and half hours, the final product having a density of 8.35g./cm. a tensile strength of 57 kp./mm. and an elongation at rupture of4% EXAMPLE 4 A prepressed workpiece was formed under a pressure of 6t./cm. from a mixture consisting of 20% finely divided chromium powder,79% carbonyl-nickel powder and 1% titanium carbide powder. The resultingprepressed workpiece was heated to 850 C. and compacted under a pressureof 8 t./cm. in a press tool preheated to 350 C. and then held constantat this temperature. The result- 3 ing product was annealed in a vacuumat 1250 C. for four and a half hours, the final product having a densityof 7.6 g./cm. a tensile strength of 30 kp./mm. an elongation at ruptureof 16.5% and a Brinell hardness of 105.

I claim:

1. A process for manufacturing high density pressformed articles from apowder mixture which consists predominantly of high alloy metals andwhich can be forged only with difiiculty, if at all, comprising thesteps of forming said powder mixture, forming a pre-pressed workpiecefrom said powder mixture, heating said workpiece to between 800 and 11000., providing a press tool for pressforming said articles, pre-heatingsaid press tool to a temperature between 150 and 350 C., holding saidpress tool constant at said temperature, and compacting said heatedworkpiece without sintering it in said press tool while said press toolis maintained at said constant temperature.

2.. A process as claimed in claim 1, wherein said prepressed workpieceis formed at a pressure of about 6 20 References Cited UNITED STATESPATENTS 2,794,241 6/1957 Dodds et al. 294205 3,089,189 5/1963 Feldman etal. 3,337,334 8/1967 Penn et al 29420.5X

JOHN CAMPBELL, Primary Examiner D. C. REILEY, Assistant Examiner U.S.Cl. X.R. 29DI'G. 31

